Flame retardant polyolefin wire insulations

Abstract

An insulated conductor and the flame retardant insulation composition used in plenum cables. The insulation composition includes as a polyolefin blend from about 50 to 85 parts by weight of polypropylene, 10 to about 40 parts by weight of a very low density polyethylene and from about 5 to about 20 parts by weight of a high and/or low density polyethylene. To one hundred parts by weight of the polyolefin blend there is about 6 to about 20 parts by weight of a chlorinated flame retardant, from about 4 to about 12 parts by weight of a flame retardant intumescent, from about 20 to 60 parts by weight of a non-halogen flame retardant, from about 0.2 to about 1.0 parts by weight of hindered phenolic stabilizer; and from about 0.1 to about 0.4 parts by weight of additional stabilizers. One of the non-halogen flame retardants in the polyolefin composition, may be zinc borate which triggers polymer and flame retardant decomposition when the polyolefin composition is exposed to an igniting flame. Alternatives to zinc borate include zinc stearate, magnesium stearate, ammonium octamolybdate (AOM), or zinc stannate.

The invention claimed is: 
     
       1. A plenum cable comprising a jacket covering a plurality of insulated conductors wherein at least one of the conductors has a flame retardant insulation composition having: a poyolefin blend comprising a mixture of polypropylene, a very low density polyethylene and a polyethylene, said polyethylene selected from the group consisting of high density polyethylene, low density polyethylene and a mixture thereof;   a mixture of flame retarding chemicals comprising a mixture of a chlorinated flame retardant and a non-halogen flame retardant; and   a hindered phenolic stabilizer.   
     
     
       2. The plenum cable of claim 1 wherein said chlorinated flame retardant is chlorinated cyclooctene. 
     
     
       3. The plenum cable of claim 1 wherein said plurality of insulated conductors comprises a plurality of twisted-pairs. 
     
     
       4. The plenum cable of claim 3 wherein both insulated conductors of said at least one twisted-pair has said flame retardant insulation composition. 
     
     
       5. The plenum cable of claim 1 wherein said non-halogen flame retardant is a mixture of a first non-halogen flame retardant, a second non-halogen flame retardant and a flame retardant intumescent. 
     
     
       6. The plenum cable of claim 5 wherein said first non-halogen flame retardant is zinc borate and said second non halogen flame retardant is magnesium hydroxide. 
     
     
       7. The plenum cable of claim 6 wherein the hindered phenolic stabilizer is a hindered phenolic stabilizer mixture of a primary and secondary hindered phenolic stabilizer with said primary hindered phenolic stabilizer being in an amount from about 0.15 to 0.5 parts by weight per hundred parts by weight of the polyolefin blend, and said secondary hindered phenolic stabilizer being in an amount from about 0.1 to about 0.5 parts by weight per hundred parts by weight of the polyolefin blend.   
     
     
       8. The plenum cable of claim 7 wherein said magnesium hydroxide is stearic acid coated magnesium hydroxide and wherein said hindered phenolic stabilizer mixture includes calcium stearate and polypropylene, and wherein the flame retardant intumescent is a silicone powder modifier which has both vinyl and acrylate functionality. 
     
     
       9. The plenum cable of claim 5 wherein said insulation composition comprises: from about 50 to about 85 parts by weight of polypropylene per hundred parts by weight of the polyolefin blend;   from about 10 to about 40 parts by weight of very low density polyethylene per hundred parts by weight of the polyolefin blend;   from about 5 to about 20 parts by weight of said polyethylene per hundred parts by weight of the polyolefin blend;   from about 6 to about 20 parts by weight of chlorinated cyclooctene per hundred parts by weight of the polyolefin blend;   from about 4 to about 12 parts by weight of a silicone modifier which has both vinyl and acrylate functionality per hundred parts by weight of the polyolefin blend;   from about 12 to 36 parts by weight of zinc borate per hundred parts by weight of the polyolefin blend;.   from about 8 to about 24 parts by weight of magnesium hydroxide per hundred parts by weight of the polyolefin blend;   from about 0.2 to about 1.0 parts by weight of hindered phenolic stabilizer per hundred parts by weight of the polyolefin blend.   
     
     
       10. The plenum cable of claim 9 wherein said insulation composition has about 70 parts by weight of polypropylene; about 10 parts by weight of high density polyethylene;   about 20 parts by weight of very low density polyethylene; and   about 12 parts of chlorinated cyclooctene.